Type of medium
Hydraulic pneumatic electrical
Hydraulic Actuators are used in industrial process control, employ hydraulic
pressure to drive an output member.
Principle : Pascal’s Law
“Pressure exerted anywhere in a confined incompressible fluid is
transmitted equally in all directions throughout the fluid, acts upon every
part of the confining vessel at right angles to its interior surfaces”.
F = PxA
WORKING OF HYDRAULIC ACTUATION SYSTEM
Case 1 Lever is moved away from valve
Α directional control valve controls the direction of oil flow in the system
and, therefore, the direction of motion of the cylinder piston.
The valve has four ports, labeled Ρ, Τ, Α, and Β. Ρ and Τ stand for pressure and tank (or
reservoir), and Α and Β are output ports. The valve can be operated in three different
case 2 Lever is moving towards valve
• The oil from the pump flows through path Ρ-Α of the valve to the upper end of the
• The oil pushes the piston downward, which lowers the attached load. At the same
time, the oil at the lower end of the cylinder flows back to the reservoir through path Β-Τ
of the directional control valve.
case 3 : Lever is idle in position
• When the directional control valve lever is released, the valve automatically returns to the
center (neutral) position.
•In this position, all four ports are blocked and oil cannot escape from either side of the
•. This stops the movement of the piston and causes oil to flow from the pump back to the
reservoir through the pressure relief valve.
A pneumatic actuator converts energy (typically in the form
of compressed Air) into motion. The motion can be rotary or
linear, depending on the type of actuator.
A Pneumatic actuator mainly consists of a piston, a cylinder, and
valves or ports.
Pneumatic systems are very common, and have much in common with
hydraulic systems with a few key differences
WORKING OF PNUEMATIC ACTUATORS
Pneumatic actuators are generally relatively simplistic and depend on their own
ability to convert potential energy into kinetic energy.
Electric motors are the most common source of torque for mobility
and/or manipulation in machines.
The physical principle of all electric motors is that when an electric
current is passed through a conductor (usually a coil of wire) placed
within a magnetic field, a force is exerted on the wire causing it to
Components Of An Electric Motor
The principle components of an electric motor are:
North and south magnetic poles to provide a strong magnetic
field. Being made of bulky ferrous material they traditionally
form the outer casing of the motor and collectively form the
An armature, which is a cylindrical ferrous core rotating
within the stator and carries a large number of windings made
from one or more conductors
Components Of An Electric Motor
A commutator, which rotates with the armature and consists
of copper contacts attached to the end of the windings
Brushes in fixed positions and in contact with the rotating
commutator contacts. They carry direct current to the
coils, resulting in the required motion
Components Of An Electric Motor (cont…)
How Do Electric Motors Work?
The classic DC motor has a rotating armature in the form of
A rotary switch called a commutator reverses the direction
of the electric current twice every cycle, to flow through the
armature so that the poles of the electromagnet push and
pull against the permanent magnets on the outside of the
As the poles of the armature electromagnet pass the poles
of the permanent magnets, the commutator reverses the
polarity of the armature electromagnet.
During that instant of switching polarity, inertia keeps the
motor going in the proper direction
A piezoelectric motor or piezo motor is a type of
electric motor based upon the change in shape of a
piezoelectric material when an electric field is applied.
Piezoelectric motors make use of the converse
piezoelectric effect whereby the material produces
acoustic or ultrasonic vibrations in order to produce a
linear or rotary motion.
A bi-laminar actuator is made from a piezoelectric
smart material that returns to its original shape
after a force is to applied to it.
“A flexing or bending actuator is designed to
produce a relatively large mechanical deflection
in response to an electrical signal.”
“Two thin strips of piezoelectric ceramic are
bonded together, usually with the direction of
polarization coinciding, and are electrically
connected in parallel.”
Basic Working Principle (cont.)
“When electrical input is applied, one ceramic
layer expands and the other contracts, causing
the actuator to flex.”
+ - + -
V-Shaped Thermal Actuators
These actuators are based on the constrained thermal expansion of
the angled beams (a result of Joule heating when a current is passed
through the legs of the actuator), resulting in motion of the center
shuttle in the direction shown by the arrow in the figure.
W.Bolton; 1995, A Text book on “Mechatronics
Electronic Control Systems in Mechanical and
Electrical Engineering” Third edition; Pearson
“Practical's in Hydraulic Systems” written by Ravi
Doddannavar and Andries Barnard, Elsevier Science
& Technology Books Publications.
The Mechatronics Handbook” written by Robert H.
Bishop, The University of Texas at Austin, Texas.
Y. Bar-Cohen, Electroactive polymer (EAP) Actuators
as artificial muscles. Reality, potential, and
Challenges, SPIE Press, Washington, USA (2001).